The Saints have spent big since returning to the Barclays Premier League and last year smashed their transfer record to recruit Ramirez from Bologna for upwards of £12m.
However, the Uruguay international struggled to fulfil expectations in his debut season and has been linked with a move away from St Mary's.
Borussia Dortmund and Atletico Madrid have been mentioned as potential destinations, but manager Pochettino has no intention to sell him.
"He's happy with us and we are counting on him for next season," he told an Italian website.
"It's normal that a lot of clubs are interested in his quality, but we don't listen to transfer rumours. We are planning for next season with him on board."
Pochettino has so far made just one summer signing, brining in Lyon centre-back Dejan Lovren for £8.5m - a move which ended interest in Cagliari centre-back Davide Astori.
"Lots of names have been linked with Southampton, perhaps too many," he added. "Some of them have been invented, others not.
"We were after Astori, for example, but in the end we went for Lovren instead. He's a great player."
Pochettino also played down talk linking Saints with a move for Astori's Cagliari team-mate Radja Nainggolan, while he also dismissed speculation surrounding a move for Osvaldo.
The Roma striker played under the Argentinian at Espanyol and reports today suggested he rejected a £17m move to the south coast.
"Osvaldo is a great player," Pochettino said. "I worked with him at Espanyol so I know what he can do.
"We are aware of his situation at Roma, but we haven't made an offer.
"We have a clear idea of what our targets should be but the market is moving very slowly at the moment. We are working prudently to reinforce the squad."